Micro-machines and micro-robots provide an option for undertaking manipulations, measurements or other functions with a high precision in structures which are difficult to access and, in particular, have small dimensions. The fields of application of micro-machines and micro-robots are diverse but are currently found predominantly in the field of production technology. However, applications in the biotechnology and medical engineering sectors are also possible. Moreover, micro-components can be used in composite materials or composite components in order to extend or improve their mechanical properties or other material properties.
A general problem relating to the use of micro-machines, micro-robots or micro-components is that of transporting them to a desired location (location of use).
Dedicated drive systems, e.g. running legs, have been disclosed for micro-robots; however, such drive systems are expensive and difficult to construct.
In the case of ferromagnetic particles, there is the option of exerting an external force thereon by way of a magnetic field gradient. As a result of this, it is possible to move the ferromagnetic particle.
In addition to the movement, the transportation to a desired location requires monitoring the current location of the ferromagnetic particle, for instance to correct the current location through further movements where necessary.
However, micro-machines, micro-robots and micro-components are often used in environments in which direct optical observation from the outside is impossible, for example because an envelope or housing blocks the observation, or else because the micro-machine, the micro-robot or the micro-component is situated in a cloudy liquid matrix. By way of example, such a cloudy liquid matrix may be a lubricating oil, a solution of non-cross-linked or partly cross-linked polymer constituents or else a slip for manufacturing ceramics. In medical fields of application, the cloudy liquid matrix may also be e.g. blood or lymph.
Magnetic resonance imaging (MRI) methods are used in diverse ways in order to obtain image information about structures. With such MRI methods, it is also possible to obtain image information from the interior of a structure without damaging the structure. By way of example, body parts of humans and animals can be imaged using such MRI methods in clinical applications.
U.S. Pat. No. 7,962,194 B2 describes a method and a system for driving and controlling the displacement of a micro-robot in a blood vessel. In one variant, the method and system determine the position of a ferromagnetic body in an object using an image recording sequence obtained with an MRI system and drive the ferromagnetic body in a desired direction to a desired target location using a magnetic field gradient generated by the MRI system, until the body has reached the desired target location. In one experimental setup, the ferromagnetic body is exposed to a liquid flow in a pipe extending through the MRI system.
However, if a magnetic particle is surrounded by a liquid matrix on the path to its location of use and needs to be moved through this liquid matrix, the position of the ferromagnetic particle in many cases cannot be reliably determined in an image recording sequence using the MRI system. The ferromagnetic particle often appears out of focus in the image and is therefore not localizable with sufficient precision in the image recording or disappears from the measurement volume altogether.
U.S. Pat. No. 8,948,841 B2 describes a method for tracking a magnetic object with an MRI system, wherein the location of the magnetic object is calculated using projections of magnetic iso-surfaces.
DE 101 42 253 C1 describes an endo-robot system which comprises a magnetic bulk field for cancelling the effect of gravity and a three-dimensional controllable gradient field for navigating the endo-robot. The endo-robot is provided for carrying out minimally invasive interventions within the body of a patient.